As fallback, I have unit-tests with a check on both correctness and the instruction count (and # of memory allocations in hot loops). Whereas the cpu cycle-coun

As fallback, I have unit-tests with a check on both correctness and the instruction count (and # of memory allocations in hot loops). Whereas the cpu cycle-count varies between runs, the instruction count does not. Linux has good support for performance counters, Windows requires a bit of work. So in this case, the compiler update would show a regression in the test suite, which needs to be addressed as part of the compiler upgrade. Of course, having this in the compiler would remove the need for unit tests.